Exposure to highly estrogenic substances can disrupt reproduction and increase cancer risk, as well as influence bone metabolism and cardiovascular health. Chemicals that are weakly estrogenic are widespread in the environment, including several pesticides. Health effects of these environmental estrogens are not known. This project is designed to determine whether a test-case exposure to environmental estrogens, i.e., exposure to dietary soybeans (rich in plant estrogens) has the expected estrogenic effects. The experimental study compares women who were randomized to a soy-diet group with women who ate normally. We are looking for changes in LH, FSH, sex hormone binding globulin, apolipoprotein A-I, and vaginal smear cytology. If plant estrogens are found to be biologically active in postmenopausal women, other questions to be addressed include: (1) What effects do these chemicals have on other segments of the population, especially premenopausal women and babies on soy formula? (2) Can plant estrogens promote carcinogenicity or, as suggested by some laboratory studies, do they have anticarcinogenic effects at least in subsets of the population, such as premenopausal women, who have high levels of endogenous estrogens? (3) Do effects of plant estrogens explain some of the differences in morbidity and mortality seen in vegetarians compared with nonvegetarians? (4) Can dietary changes be used in prevention or treatment of estrogen-related conditions?